1. Field of the Invention
This invention relates to improvements of the device for imprinting letters, numerals or other data on film frames in the camera when the exposure is made.
2. Description of the Related Art
A variety of devices for imprinting data such as the date on the film when the exposure is made have been proposed and some of them have been put into practice.
For example, U.S. Pat. No. 3,889,281 shows a proposal that the intensity of light or the lighting time of a miniature lamp or light emitting diode as the light source for imprinting data is made manually variable in view of the sensitivity of the used photographic film in order to insure that, as the data exposure is suitably corrected to the given film speed, the imprinted data are clear enough as shown in FIG. 3(a). Thus, the imprinted data are prevented from becoming unreadable due to the under-exposure as shown in FIG. 3(b), or from diffusing to a large loss in the sharpness due to the over-exposure as shown in FIG. 3(c). With this device, however, each time the type of film, and particularly the film speed, change, the photographer needs to reset the value of film speed in the data imprinting device built in the back cover of the camera by manually operating the film speed selector knob. Such a requirement is very inconvenient.
To eliminate this drawback, there has been a previous proposal that once the film sensitivity is set in the camera, or when a film cartridge having information codes for the sensitivity is loaded in the camera, the exposure factor for the data imprinting device is automatically taken at a suitable value to the sensitivity of the used film, as, for example, disclosed in U.S Pat. No. 4,420,236.
However, in the above-described examples of the prior art, the exposure correction factor setting means of the camera is operated in accordance with the desired picture quality of the photographer when shooting. In the exposure value computing circuit of the camera, the preset film sensitivity information and the desired value of the exposure correction factor can both be taken into account in deriving an exposure value, i.e. aperture value (Av) or shutter time (Tv) from the brightness of the object to be photographed so that a desired result or a picture can be attained. But, in the data imprinting device, only the film sensitivity information is given and the data exposure is not corrected in accompaniment with the change of the exposure correction factor.
Therefore, if the exposure correction of the camera is operated in a direction to increase the exposure, the photographic light amount (the exposure of the camera) increases despite the preset film sensitivity remaining constant. But, in the data imprinting device, because the exposure of letters or the like is made based on the preset film sensitivity, ignoring the aforesaid exposure correction, the data imprinting light amount becomes insufficient relative to the photographic light amount. This has constituted a problem of failing to imprint clear images of the data.